High frequency electrical apparatus



Feb. 3, 1942. R. H. VARIAN ETAL 2,272,155

HIGH FREQUENCY ELECTRICAL APPARATUS Filed March 1, 1938 '7 Sheets-Sheet 1 INVENTORS Feb. 3, 1942. R. H. vAmAN ET AL HIGH FREQUENCY TJLHCTRIGAL APPARATUS Filed March 3,, 1938 '7 Sheets-Sheet 2 INVENTORS Feb. 3, 1942. R. H. VARIAN ETAL HIGH FREQUENCY ELECTRICAL APPARATUS Filed March 1, 1958 7 Sheets-Sheet 3 INVENTORS MA/%A M LA Feb. 3, 1942.

R. H. VARIAN ETAL HIGH FREQUENCY ELECTRICAL APPARATUS Filed March 1, 1938 as bowao a '7 Sheets-Sheet 4 Feb 3, 1942..

R. H. VARIAN EI'AL 2,272,165

HIGH FREQUENCY ELECTRICAL APPARATUS Filed March 1, 1938 '7 Sheets-Sheet 5 INVENTORS Feb. 3, 1942.

R. H. VARIAN ETAL HIGH FREQUENCY ELECTRICAL APPARATUS Filed March 1, 1938 '7 Sheets-Sheet 6 Feb. 3, 1942. R. H. VARIAN EI'AL 2,272,165

HIGH FREQUENCY ELECTRICAL AFPARATUS Filed March 1, 1958 7 Sheets-Sheet '7 lli l F/g. 9A

{Ross JEWO/V A-A). I

INVENTORS v LMXLLL A. MM

Patented Feb. 3, 1942 FREQUENCY arnc'rnrcar.

APPARATUS Russell H.

Varian, William W. Hansen, and

lldsay M. Applegate, Stanford University,

6 z. the

.21 asslgnors to The Board of Trustees of Leland Stanford Junior University, Stanford University, Qalifl, a corporation of Callfoa Application March 1, 1938, Serial No. 193,263 I (ill. 25li--36) 16 Claims.

The present invention relates, generally, to the control of electron beams by electromagnetic fields for the excitation of electric circuits, and has reference, in particular, to novel electrical high frequency apparatus in which electron beams are subjected to displacement by electromagnetic fields confined in hollow conductors or in conductor arrangements capable of maintaining standing electromagnetic waves.

The embodiments of the present invention utilize some of the elements of Patent No. 2,190,712, William W. Hansen, February 20, 1940, and Patent No. 2,242,275, Russell H. Varian, May 20, 1941, to which patents the present invention is related.

In Patent 2,190,712 there is disclosed a hollow conducting resonant chamber of novel type having characteristics that render the same particularly adaptable to use in providing oscillating circuits having frequencies of the order of cycles or more per second. When operating at frequencies of the order of 10 cycles per second such resonant circuits are of outstanding importance. In the present invention this type of circuit is used as shown in the drawings because of its convenience and usefulness. The present invention can be embodied without the special resonant circuits or the above-mentioned Patent No. 2,190,712 but not in general without some sacrifice of convenience and eflicienc'y. The enclosed resonant circuit of said Patent No. 2,190,712 has come to be known by the name rhumbatron, a word coined from Greek words meaning "rhythm and thing." The rhumbatron is essentially a hollow chamber with conducting walls capable, together with coupled apparatus, of sustain ng electromagnetic oscillations as a very emcient resonant circuit. It is distinguished from other types of oscillating circuits by its mode of operation even more than by its appearance. It operates so that an electromagnetic field is produced inside the closed conducting chamber by currents confined to the walls of the chamber surrounding the contained field. In the following description, the word rhurnbatron will be used to designate a resonant circuit of the type shown in Patent No. 2,190,712.

In Patent No. 2,242,275 there is disclosed means for controlling a beam of electrons by causing it to pass through an electric field, particularly a field with its electric component parallel to the axis of the electron beam to which is parallel also the axis of a rhumbatron containing the field. Such a beam is made to produce radio frequency oscillations.- That invention includes among other things the combination of a rhumbatron" and a beam of electrons passing through it for control purposes. The present invention uses this combination in some embodiments thereof. The invention of Patent No. 2,242,275 has come to be known by a coined word klystron" derived from two Greek words meaning waves breaking on the beach and thing.

This invention has for its principal object the provision of a novel high frequency electrical apparatus adapted for the excitation of electric circuits by periodically transversely, radially, or rotationally displacing an electron beam, the displacement of which requires less power than that rendered available as high frequency energy as the result of the deflection of the beam, whereby the energy of an. electron beam is converted into an alternating current of any desired high frequency.

Another object of the present invention is to provide novel apparatus for the control of electron beams by causing transverse types of displacement, resulting in the excitation of circuits by beams periodically transversely displaced, and the amplification of power by the use of transversely displaced electron beams in suitable circuits.

Still another object of the present invention is the provision of a novel high frequency electrical apparatus with associated circuits for performing all the principal functional operations ordinarily associated with the generation, amplification, modulation, transmission, reception and detection of high frequency oscillations.

Otherobjects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is a diagrammaticrepresentation of an embodiment of our invention using a hollow resonator to change the velocity of an electron beam and a magnetic field for its lateral deflection.

Fig. 2 is an embodiment similar to Figure 1, except that an electric field is used for beam deflection.

Fig. 3 is an embodiment in which an electron beam is given radial displacement as a result of variation of beam velocity by a hollow resonator.

Fig. 4 is an embodiment in which an electron beam is displaced laterally by one hollow resonator and alternating energy absorbed in another such resonator.

Fig. is a circuit diagram for the explanation of Fig. 4.

Fig. 6 is an embodiment in which an electron beam is initially given lateral displacement by a hollow resonator and electric fields are then used to change the velocities of the electrons of the beam thereby converting transverse movement of the beam to density modulation of the electrons and then absorbing energy from the beam by use of a second hollow resonator.

Fig. 7A is an embodiment of our invention and a showing of one of its applications in which an electron beam is laterally displaced in an electric field, so that the energy of which beam is absorbed in maintaining an electromagnetic field in a hollow resonator, which field is used for accelerating electrons.

Fig. 7B is a simplification of the structure of Fig. 7A.

Fig. 8 is an embodiment in which an electron beam is given periodic lateral displacement and caused to enter a resonator at an oblique angle to set up and maintain oscillations therein.

Fig. 9A is an embodiment in which an electron beam is given simultaneous transverse and rotational velocities in a steady magnetic field superimposed on a hollow resonator electric field,

. and

, Figs. 9B, 9C and 9D are details of construction. Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Fig. 1, an emitter of electrons I, shown as of the oxide-coated type, produces a plurality of electron beams 2 from act1ve areas 3 of the emitting surface. The electrons are accelerated by a polarized grid 4 and they pass through the field between the spaced grids 5 of a "rhumbatron" or hollow resonator 6 coupled by interconnected inductiv loops I and 8 to a second hollow resonator 9. The electron beams 2 after passing through the field of resonator 9 traverse a magnetic field extending at right angles to the direction of travel of the electrons. The magnetic field is produced by a magnet I I which in Fig. 1 has a location such that one of the pole faces of the magnet faces the observer. The magnetic lines of fiux are visualized as coming out of the pole face perpendicular to the plane of the drawing. The magnetic field has the property of turning the electrons in the stream through an arc of 180 degrees, the radius of the are being proportional to the velocity of the electrons at the voltages ordinarily used. The electron beams after leaving the magnetic field of magnet it pass into resonator 9 through openings H2. The electrons are stopped and absorbed by a coupling plate l3 at the potential of polarized grid d. Their energy is substantially absorbed by the field electromagnetic field existing between the openings l2 and the plate !3 in the manner explained in the above identified applications.

In the operation of Fig. 1 the electron beams are acted upon by the alternating electric field between the grids 5 of resonator 6. This field alternately increases and decreases the velocities of the electrons in successive portions of the streams and as a result of the changes in the velocities the radii of curvature of the paths of the electrons in the field of magnet ll increase and decrease. Accordingly the beams where they leave the magnetic field oscillate across the openings l2 in a direction corresponding to that which is up and down on the drawing and transverse to the axis of the beams. This is indicatedby the solid and the dot-dash lines indicating the outer and inner edges of the beams where they enter the openings l2. Each of the three beams shown oscillates in the range between the solid and dotdash lines. The beams are each just the width of the corresponding openings 12 so that when they are at the positions corresponding to maximum velocity, that is with their outer edges at the solid lines, substantially all electrons enter the openings l2. When the beams have shifted to the positions corresponding to the minimum velocity, that is, with their inner edges at the dot-dash lines, substantially none of the electrons enter the Opening l2. The beams thus are alternately allowed to pass through the openings l2 and prevented from passing by being blocked by the wall area extending between the openings l2 and hence electrons enter the field of resonator 9 in alternate half cycles. The electrons enter the electromagnetic field extending between the openings I2 of the resonator 9 and the plate 13 thereof during the alternate half cycles when the field therein opposes the motion of the electrons and they hence deliver energy to this field which causes the resonator to oscillate.

The portion of plate l3 struck by the electrons may be either solid or perforated inasmuch as the work is done by the electrons on the field between the plate and the outer Wall of the resonator 9 rather than on the plate itself. A portion of the energy from resonator 9 is conveyed by loops 8 and I to resonator 6 for its excitation. The advantage of using a plurality of electron beams instead of a single beam is that less displacement is required to shift a narrow beam the necessary distance for cutting it than is required by a wide beam. Thus, a large total electron emission can be controlled without a very large excitation in resonator 6. If desired, all the beams may be focused at a single slot by having them pass only through the magnetic field instead of as shown. In this case the resonator 9 would be set at right angles to its present position shown in Fig. 1.

The arrangement shown in Fig. 1 can be used as a self-excited oscillator as just described, or it may be used as an amplifier or detector. For use as an amplifier energy is introduced into resonator 6 by an inductively coupled loop l4 fed as from an antenna or by a capacitively coupled element N). If the loop is used it is placed so a component of its area is perpendicular to the lines of magnetic flux in the resonator. If the capacitive element is used it is placed so an electric field is produced between it and a wall of the resonator superimposed on the resonator electric field. The same principles of coupling apply, of course, to the use of loops 1 and 8 and plate I3 in resonator 9 when the apparatus is used as an oscillator. The excitation of resonator 6 by a signal of suitable frequency introduced by loop [4 or element It! results in changes of velocity of the electrons of the beams. The beams consequently swing as described previously where resonator 6 was excited by the coupling loop I. Coupling loops 1 and 8 feeding back energy from resonator 9 to resonator 6 make the system regenerative, and may be omitted if desired.

An arrangement similar to Fig. 1 but using an electric field instead of a magnetic field to turn the electron stream is shown in Fig. 2. All the numbered elements in Fig. 2 are the same as in Fig. 1 except for the following difierences. The emitter 3 produces a single beam of electrons.

There is but a single opening l2 in the resonator 9. Instead of using the magnet ll of Fig. 1, two electrostatic field plates 68 and H bent to the arcs of circles are used. If the paths of the electrons are parallel when they enter the electric field between plates It and ii they will be tumed' so that they cometo a focus after being turned approximately through 80 degrees. By placing the slot it at this angle a relatively heavy intermittent current of electrons can be conducted through a small opening. Changes in velocity of the electrons due to the action of resonator 8 cause them to sweep back and forth into and away from the slot E? a shown in full and dotted lines in Fig. 2. The resonator 9 is thereby caused to oscillate and to excite the resonator 8 as explained in connection with Fig. 1. An important advantage of the arrangement shown in Fig. 2 is that the dimensions transverse to the electron beam of slot i2 and corresponding parts of the system can be kept small while the dimensionsalong the slot that are perpendicular to the plane of the drawings can be made as great as desired to accommodate whatever power is necessary.

In Fig. 2 there is, in addition to the elements described thus far, an apertured plate It and a grid it which is shown placed in front of the opening l2. Grid i9 is connected to the exterior of resonator 9 which is at positive potential with respect to the emitter 5 due to the ground connection shown. The plate It is connected back to a point in the accelerating battery at a potential but a little positive with respect to the emitter i'. An electron that comes through grid i9 is decelerated as it approaches plate it so that its energy is materially reduced by the time it enters the opening in plate it. Emerging from the hole in plate i8 it is accelerated again to the same Velocity it had when it encountered grid it. Its energy is delivered to the field between the top of the resonator 9 and the coupling plate it inside in the same manner as described in connection with Fig. 1. The electrons that are deflected so they do not go through the opening in plate it are stopped on the plate. They will have been decelerated before they hit the plate so that energy will have been absorbed in the field between grid it and plate it. The electrons that hit plate it will be conducted back to the battery at nearly zero potential and their energy thus will have been regained and returned to the circuit instead of having been dissipated as heat on the top of the resonator ii as would occur in the absence of plate i3 and grid iii and as shown in Fig. l. The plate 98 and grid it? are applicable, obviously, to the embodiment shown in Fig. l or to any other embodiment where an electron beam is utilized by transverse displacement for circuit excitation during alternate half cycles.

Obviously the electrostatic field plates it and it could be carried through twice the angle shown in Fig. 2 in a way corresponding to the 180 magnet shown in Fig. i. In such an arrangement the electron beam would be formed into an image of its initial form after traversing an angle of about 160. The beam in operation would be shifted across a slot in a manner similar to that of Fig. i. This arrangement of Fig. 2 when passing the electrons through a 160 turn has a particular advantage of high frequency stability. Its stability results from the conditions of operation possible in the electrostatic field. The field between plates l6 and I1 requires very little energy and consequently can be held easily to a predetermined difference of potential. The time required by an electron to traverse the length of the fleld between plates it and I1. assuming these plates to extend through of arc is determined by the inherent properties of charge and mass of the electron and is substantially independent of the electron accelerating voltage. Minor changes in the voltage on the electron beam merely shift the entire beam transversely small amounts that. may reduce the effective area of the beam slightly but will not sheet the frequency. The frequency then is determined substantially entirely by the properties of resonator 6 and the rest of the resonant circuit. The sharpness of frequency determination in hollow resonator circuits is very high, particularly when a resonator is operating on a harmonic of its fundamental. Accordingly, since the disturbing factors of voltage regulation are eliminated, the frequency will not vary ap-- preciably in ordinary modes of operation.

If extreme frequency stability is desired, resonators 6 and 9 are made to oscillate on their fundamental frequency and a third resonator is employed having a lower frequency fundamental but operated on one of its harmonic frequencies. and coupled to resonator t or between resonators t and d, the same being introduced into the leads extending between coupling loops l and 8.

An important consideration in the transfer of energy between electric circuits is that of matching the impedances of the circuits. This applies when one of the circuits contains a beam of electrons as well as to ordinary circuits. The electron impedance of a beam of electrons is defined as where Va is the direct current accelerating potential difference associated with the beam, and Is is the electron current. The power through a resonant circuit, including losses and energy transmitted to outside loads is where V: is the voltage across the circuit and Er is the effective impedance of the circuit at resonance. The power extracted from the beam by the circuit is expressed as VrIr and the power of the electron beam is veIe where I! is the root mean square value of the current in the resonant circuit and Ie is the electron beam current. We have found that the relationship of Ir which is an. alternating current and Ie which is a direct electron beam current is expressible by the series:

Ir=Ie[1+2ai cos (wt-H31) +2012 cos mart-H32) .1

where :21 is the ratio of the first harmonic component of 11' to Ie, s1 is a phase angle related to the first harmonic current, and a2 and iii are factors relating to the second harmonic. The power of the circuit is:

where T is the time of one cycle, V is the instantaneous voltage of the resonant circuit and I the instantaneous current. This is equal to P=%,J-2 v.1, f cos(wt+ s 1 +2. cos(wt+ 5 .14: which when integrated=\/zVrIa.

Other calculations we have performed indicate that the factor cu in some embodiments of our inventions will approximate 0.58. Some of our experimental apparatus has been found to operate satisfactorily with or of the order of 0.3. The actual value of this factor is subject to other factors and may be either higher or lower than the values stated under some conditions. The energy put into the resonant circuit, V2V1Ia1, must be equal to the power used there,

For maximum efiiciency we want Vr=0.707V, that is, the peak radio'frequency voltage equal to the electron voltage. If this condition is to hold, R1 is determined as 1 V. 1 *m 1171 We may note that, if this condition on R: is fulfilled the ratio of direct current electron beam power to radio frequency power supplied to the resonant circuit is on. With a1=0.5 which is a reasonable value to assume, the impedance of the hollow resonator loaded is sufiiciently high and substantially equal to the beam impedance.

An example of a beam actually used is one with a voltage of 3000 and a current of.0.03 ampere. This gives a beam impedance of 100,000 ohms. A circuit employing a hollow resonator with a no-load impedance of 1,000,000 ohms can have its impedance reduced by the introduction of load or radiation resistance to a much lower value, for example 100,000 ohms, under which conditions nine-tenths of the energy would be transferred from the circuit to the load and the efficiency would be 90 per cent.

A further reason for using the hollow resonator type circuit in our invention is that linear conductor circuits become so small in their physical dimensions at frequencies of the order of cycles per second that the attachment of grids for producing uniform fields of practical dimensions is unsatisfactory whereas the hollow resonator can easily be formed to accommodate grids and to produce substantially uniform fields of areas large enough for the transfer of comparatively large amounts of energy.

Fig. 3 shows an arrangement of our invention wherein a focused stream of electrons passes through a hollow resonator and is subjected to periodic changes in velocity, with consequent periodic focal displacement. In this arrangement, the beam is focused to a point and the transverse displacement instead of being in only one direction as in Figs. 1 and 2 is radial in all directions. This is accomplished by focusing the beam with a magnetic field parallel to the axis of the beam. In Fig. 3, 2| is a focusing source of electrons, and 22 is an accelerating plate through which the accelerated electrons pass. The electrons come from the source 2| in converging rays and they are focused where they pass through the plate 22. They diverge after emerging from plate 22 and are focused by the field of a coil 23 concentric with the axis of the'electron beam. A hollow resonator 24 is placed at this focus. The electrons pass through the field of resonator 24 at its center and again diverge and again become focused in the region of a second resonator 25. Resonator 24 alternately accelerates and dec' lerates successive portions of the electron beam passing through it; This causes the point of focus in the region of resonator 25 to shift along the axis of the beam at varying distances from the resonator 24. The entrance for the electrons in resonator 25 is a comparatively small hole so that when the focus is very far away from it the area of the electron beam at the opening will be materially larger than the opening. Thus, when the focus is displaced longitudinally a little way from the opening, only a relatively small portion of the electrons will enter the hole in member 25. The result is that the resonator 25 receives electrons at a periodically varying rate.

This arrangement is subject to several modes of operation depending upon its adjustment. First as a simple amplifier, a coupling loop 26 fed as from an antenna can be employed in resonator 24 to supply energy substantially at the common frequency of the two resonators 24 and 25, thereby controlling the beam at that frequency. The distance from the resonator 24 to resonator 25 is adjusted so that the electron beam without any input energy from loop 26 is focused a little way from resonator 25 toward resonator 24. Now when the beam is excited the focus will oscillate along its axis about the static focal point. Thus, when the velocity of the electrons is increased due to the action of resonator 24 above the static velocity the focus will move toward resonator 25 and it will receive an increasing number of electrons and conversely when the velocity is decreased by resonator 24 the number of electrons entering resonator 25 will decrease. Accordingly member 25 may be excited by pulses of electrons occuring each cycle of oscillation. The amplified energy will be removed by a coupling loop 21. For operation as a simple amplifier the two coupling loops 28 and 29 are omitted.

Second, this apparatus will operate as a selfoscillator. In general, any amplifier will oscillate if feed-back of energy in correct phase occurs between the controlling and the controlled circuits. This is true also here where the addition of connected coupling loops 28 and 29 between the resonators will cause the system to oscillate. For oscillation of this kind the electron beam is adjusted as for amplification.

Third, the arrangement of Fig. 3 will act as a frequency doubler. To accomplish this the system is excited by energy introduced in loop 26. The electron beam is focused so that when it is not oscillating the focus is at the hole in resonator 25, and in oscillation it will move in and out through the hole. Thus, oscillation in resonator 24 will cause the beam to spread out over the hole in resonator 25 twice each cycle of oscillation in resonator 24. Accordingly resonator 25 is subjected to electron pulsation of double the frequency of the resonator 24. Resonator 25 is made resonant to a frequency double that of resonator 24 and hence its output is at twice the input frequency of the system.

Obviously, the plate l8 and grid l9 used for salvaging the energy of the unused electrons in Fig. 2 can be applied to Fig, 3 as well as to Figs. 1 and 2, is desired.

Figs. 1, 2, and 3 show embodiments of our invention having, in common, the control of an electron beam by passing it longitudinally through an electric field thereby changing the velocities of electrons in the beams and using the variation in velocity to efiect transverse displacement of the beams, while Figures 4 through 8 show arrangements in which an electron beam is controlled by passing it transversely through an electric field thereby giving it directly a peria second resonator M through openings in their common wall 42, impinging finally on faces M and 41' of member 4| which faces are separated by a slot 48. An input coupling loop 43 is provided in resonator 31, an output loop 44 in rhumbatron ti and feed-back coupling loops 45 and 46 in 31 and M, respectively. The electrical equivalents of the parts of Fig. 4 are shown schematically in Fig. 5.

In the operation of Figs. 4 and 5 the electron beam is deflected alternately first toward the face 39 and then toward the other face 39'. The beam thus impinges alternately on the two faces 41. M of member M. The resonator 31 needs only enough energy to provide sufiicient controlling electric field between the faces 39, 35C. Energy of the electron beam is absorbed in the field between the wall 42 and the faces M, 41' of member M. When the beam enters the field adjacent to the upper face 61' an increment of current is introduced in one direction in the resonant circuit and when it enters the field at the lower face M an increment is introduced in the opposite direction. The action of the coupling loops in Figs. 4 and 5 operate as described for the corresponding loops in the preceding figures.

The resonator in Fig. 4 are shown with the ends toward the observer'cut away for illustrative purposes. Actually the are preferably made symmetrical and closed at both ends. They can be made as long as may be desired to accommodate a large beam of electrons of small dimensions in the direction of its periodi displacement. The current in 31 circulates around the inside surfaces of the conducting shell, of which the resonator is composed, from one face 39 or 39' to the other and back. The magnetic field is distributed so the lines of flux are substantially parallel to the contours of the conducting shell. The electric field is also distributed but it is developed to a fairly uniform high intensity between the faces 39, 39'. The dimensions of the faces along the axis of the electron beam, for best operation, are restricted to the distance the electrons go in a half cycle or less. The resonator 4| is similar to 31 except that in 4! nc uniform electric field is necessary and a reduced capacity is desired so that faces 41, 41' are brought to narrow edges at slot 48 so they can be put close together without having excessive concentrated capacitance. In resonator 4! there are considerable components of electric field between the faces 41 and 41'. This is illustrated in Fig. 5 in which the capacitance between the faces 41, 41' isindicated by the condenser part of the circuit 4|. The faces 39, 39 of resonator 31 of course constitute the capacitance of that part of the equivalent circuit. The correspondence between the parts of Figs. 4 and 5 follows clearly from the numerical references.

In Fig. 5 the electron beam is shown in outline and discontinuous on the two sides representing the limits of its transverse deflection. This illustration is intended to convey the idea of what actually takes place when the electron beam is periodically displaced transversely. The illustration is precisely correct for the hypothetical case of square wave excitation of the plates 39. 39'. .For such excitation, a block of electrons for one half cycle would be directed toward the upper plate while for the alternate half cycle they would be directed toward the lower plate. with sinusoidal excitation the beam resembles a stream of water from a hose the outlet of which is moved up and down, the stream of water being intermittent at the same frequency as the 7 up and down motion or the outlet. The electron beam can be visualized as a wavy stream splashing on first one and then the other of plates 41, 41'. Inasmuch as this explanation will enable one skilled in this art tounderstand what ocours in the operation or our invention, the figures have all been drawn for convenience indicating the outline of the beams.

In the embodiment of the present invention shown in Fig. 6 an electron beam is subjected to periodic transverse displacement and thereafter through use of suitable electron fields caused to become density modulated, i. e. of varying density from point to point along its length. Said modulated beam is then used for exciting a hollow resonator.

In the figure, an electron beam from an-emitter 5| enters a resonator 53 through openings 52 in its wall. The beam passes between the internal faces 54 of resonator 53 whereby an oscillating electric field is impressed upon the electron beam as described in Fig. 4. The beam traverses member 53 and exits through'grid opening 55 where it enters an electrostatic field between grid 55 and an oblique grid 56 maintained by the battery shown. A second electrostatic field is maintained between another oblique grid 51 and a transverse grid 58. After leaving the field through grid 58 the electrons enter an alternating field between spaced grids Si or a second resonator 59. The two resonators 53 and 59 are shown coupled together by coupling loops 62 and 63 in the manner indicated in the other figures.

In operation, the electron beam is periodically shifted from side to side so that it moves in the way represented in Fig. 6 from right to left and reverse as it passes downward through grids 55 to 58. Grids 55 and 5B are both preferably positive with reference to th electron emitter. Grids 56 and 51 are both at a potential materially different from that of grids 55 and 58, preferably only slightly positive in reference to the electron emitter. An electron entering the field between grids 55 and 56 is either accelerated or decel erated depending upon the relative polarity of grids 55 and 56. For convenience it will be assumed that grids 56 and 51 are negative in respect to grids 55 and 58. Then an electron will be decelerated in the space between grids 55 and 56. Its velocity will be unafiected between grids 56 and 51 and it will be accelerated between grids 51 and 58. The resultant change in velocity between grid 55 and grid 58 will be zero. However, the time taken by an electron in transit from grid 55 to grid 58 will vary depending upon its transverse position in the fields the electron traverses. If it is toward the left side of the beam as represented in the drawing, and grids 56 and 51 are negative with respect to grids 55 and 58, the electron is very quickly decelerated and it travels at the reduced velocity the comparatively long distance from grid 56 to grid 51. Between grids 51 and 58 it is quickly accelerated to its original speed. If it is located toward the right side of the beam the electron will be more gradually decelerated in the space between grids 55 and 56. It will travel a relatively short distance between grids 56 and 51 at the reduced speed and it will be relatively slowly accelerated to its original speed between grids 51 and 58. Thus, it will take less time for the electron to go from grid 55 to grid 58 in a region where grids 55 and 51 are close together than where they are farther apart. The reverse is true if the outer grids are made negative and the inner ones positive. When the electron beam is oscilatting laterally some electrons will get from the emitter to the region beyond grid 58 in less time than others. The result is that the transit time from grid 55 to grid 58 is a function of beam deflection, and it is possible for electrons leaving grid 55 after some other electrons to have a shorter travel time between the emitter and grid 58 and to arrive at grid 58 at the same time as those that left the emitter earlier, thus forming a periodic electron concentration. This has the effect of making the elec- 7 tron stream where it leaves grid 58 periodically non-uniform that is grouped or bunched. The electron beam travels on and enters the field between the spaced grids SI of a rhumbatron 59 Which is caused to oscillate by the bunched electron beam as explained in Patent 2,190,712. In the terminology used hegein in apparatus of this kind, the means included between the emitter 5i and grid 58 in Fig. 6 is called a buncher. Its function is briefly set forth as that of converting a substantially uniform electron beam, or one varying at low frequency, into one that varies in density, that is, grouped, at high frequency. The oscillating resonator 59 delivers energy to the buncher through the interconnected coupling loops 82 and 53.

Another embodiment of our invention using an electron beam given periodic transverse displacement for control is shown in Figs. 7A and 7B. In Fig. 7A a beam of electrons is accelerated from an emitter II by a grid 72 and is projected between a pair of deflecting plates M and 15 into a resonator 16 where the electrons impinge alternately on two plates Ti and 18 after entering through grid 88". The electron beam is shifted from one plate to the other by an alternating field caused to exist between plates 74 and 15 which receive excitation from a loop l9 inside resonator I6 and a symmetrically arranged pair of leads 8! and 82 outside the resonator. These leads would ordinarily be close together or in the form of a concentric line but are shown far apart for convenience in the drawing. The energy of the electron beam is coupled into the resonator 16 by a pair of coupling loops 83 and 84 connected to the plates 77 and 18.

The process of oscillation of Fig. 7A is similar to that of Fig. 4 except that in Fig. 7A the electron beam energy is absorbed alternately in the fields between grid 88" and the plates 11 and 78 conveying pulses of energy alternately to the coupling loops 83 and 84. The arrangement provides a pulsation of current in the loops 83 and 84 every half cycle, the alternate pulsations being of opposite polarity.

Resonator T6 is illustrated as a right circular cylinder whose axis is horizontal and transverse of the figure. The faces 80 and 89' in such case are circular and they are at a uniform distance apart as the heads of a drum. The openings where the electron beam I3 enters are in the curved side of the drum-shaped container. In

it, the electric field exists most strongly in the center extending from side to side in the figure, across the space between the two sides and 80'. The magnetic field in the resonator at a section corresponding to that of the plane of the drawing exists perpendicularly to the plane of the drawing and is strongest near the curved sides of the resonator, where it is interlinked with the coupling loops. The elements H to 84, inclusive, cause, as a result of powerful oscillations in the resonator 16, high alternating differences of potential to exist between the side 88 and side 89' of the resonator 16. This difference of potential is used to accelerate electrons to high velocity for various applications one of which is illustrated.

An electron emitter 9| and an accelerating grid 92 project a stream of electrons 93 between two deflecting plates 94 and 95 into the resonator 16 through an opening in the side 80. If the resonator is oscillating, the plates 94 and excited thereby will swing the beam of electrons 93 back and forth so that during alternate half cycles the electrons will alternately miss and enter the hole 85 in the side 88 of the resonator. The polarity of the plates 94 and 95 is arranged so that the electrons enter and pass through the resonator during the half cycles when the integrated value of the accelerating force on an electron is a maximum. This occurs generally when the electrons are admitted to the hole 85 of resonator 16 just as the other side 80 thereof begins to accumulate a positive charge. The potential difference between the grid 92 and the emitter 9! is made great enough so that the elec-- trons enter the resonator with a fairly high velocity and preferably of the order of nine-tenths of the velocity of light.

The dimension of the resonator 18 from the side 88 to the side 89' is made a little less than the distance a particle with the speed of light will travel in a half period of the resonator oscillation. Thus, any electron whose velocity approaches that of light can make several circuits from side to side of the resonator l8 and back without getting out of phase with the oscillations of the system inasmuch as the maximum velocity any electron can attain will be less than that of light. An electron admitted to the resonator through the hole 85 crosses the resonator and reaches the side 88 in about a half period. It passes through the hole 88 and enters the field of a magnet 96 where its motion is reversed. The electron, after the direction of its motion has been reversed, by the field of magnet 96, re-enters the resonator 16 through a hole 88'. The electron then travels back to the side 89 and through a hole 85' in the next half period and is reflected again by a second magnet 91. This is repeated as many times as required to get the electron velocity desired. In Fig. 7A there are three reflections at the side 80 and two at the side 80 of the member I6. After the last refiection at the side 80' through an aperture 85'-' in side 80 and passing below magnet 91 impinges upon a target 98 where the impact is shown for producing X-rays.

Fig. 7B shows an arrangement for producing X-rays using only a single trip of the beam through the resonator 76 for the acceleration of electrons. The structure of Fig. 7B is similar to the electron passes that of 7A except for the different mechanical arrangement resulting from the omission of the magnets 96 and 91.

In Fig. 8 the interaction of a periodically accelerated transversely and radially. A third transversely displaced uniform electron beam and an electric field obliquely disposed relative to the axis of the beam excites a circuit connected with the electric field. In this figure a beam of electrons is produced by an emitter IOI, accelerated by a grid I02, and projected between a pair of deflecting plates I03 into an electric field between a grid I04 and a plate I which are parts f a resonator I06. The plates I03 are excited by connection to a coupling loop I01 in the resonator.

In operation, the electron beam swings back and forth between the plates I03, from left to right and reverse in the drawing. The dimensional relationships of the principal parts of the arrangement shown in Fig. 8 are such that the difference between the time of travel of an electron from the plates I03 to the edge of grid I 04 at the left side of the beam and the time from plates I03 to the edge of grid I04 at the right side is about equal to the time required for the electron beam to sweep over the grid from the left end to the right end, The effect is that duringthe half cycle when the beam swings from left to right the electrons projected toward the grid I04 as the beam moves toward the right will all arrive at the grid at about the time the beam has reached the right hand edge of the grid I04. Thus, a large number of electrons enter the field between the grid I04 and the plate I05 in an interval only a fraction of a half period long. As the beam moves back toward the left, the disstances the electrons have to travel to get to the grid I04 increase with the time so by the time the beam has reached the left edge of the grid I04 all the electrons to the right of the beam will have entered the field between grid I04 and plate I05. The effect is that during the half cycle of beam shift from left to right the entrance of the electrons into grid I04 is delayed to the end of the half cycle but that during the half cycle while the beam travels from right to left there is no delay. Accordingly the entrance of electrons into the field between grid I04 and plate I05 is accomplished at the beginning of and during alternate half cycles. This is the same in effect as if the electrons were delivered in a bunch each cycle, and is of course a condition sufiicient for the excitation of a resonant circuit.

It will be noticed in Fig. 8 that the grid I04 and the plate I05 are shown as curved, although they may be made straight. The straight lines are the most convenient to make and are sufficient for operation; but when it is desired to regulate the relationship of the time of entry of electrons along the grid I 04 in regard to the time the beam arrives in its transverse motion at specified places along the grid, the grids are curved to accomplish the desired time relationship and to increase the efficiency of utilization of the beam. In the illustration, the sinusoidal curve is intended to make the bunching more sharply defined by having the rate of change of distance from plates I03 to grid I04 inversely proportional to the velocity of sweep of the beam in its transverse movement. This is somewhat sinusoidal, as in simple harmonic motion, and accordingly the curve of the grid I04 and plate I05 surfaces is of sinusoidal form. The principles of excitation involved in resonator I06 are similar to those in rhumbatron 9 in Fig. 1 and 59 in Fig. 6 and are explained with reference to the above referred to patents.

In Figs. 1 to 8 we have shown our invention in embodiments in which electron beams were type of acceleration is shown in Figs. 9A to 9D in which rotational transverse velocities are imparted to the beam. A stream of electrons is accelerated from an emitter I II through an electrode H2 and through an evacuated tube H3. The tube II3 extends through a magnetic field parallel to the tube axis and of uniform strength across the tube, the magnetic field being produced between the poles H4 and 5 of a magnet H6. Superimposed on the magnetic field at right angles to it there is an alternating electric field produced by an oscillating resonator III, excited by a coupling coil H8. Where the tube H3 passes through the magnet poles H4 and H5 there are coils H9 and I2! concentric with tube II3 that are to maintain uniformity of field in the direction of the length of tube II3 over the entire cross-section of the holes where the tube II3 goes through. These coils make it possible to have a uniform magnetic field with the magnetic flux in the direction of the axis of the tube II3 over its entire cross-section. Facing the end of the tube H3 where it leaves the magnet pole II5 there is a plate I22 with a 'hole I23 in it. Beyond plate I22 is a solid plate I24. These two plates are enclosed in an enlarged extension of tube H3. Plates I22 and I24 are connected to an amplifier I25 that can be of any suitable form or it can be a receiver I26, shown in Fig. 9B. The plate I22 is made either with a round hole I23 as shown at 9C or with a hole of approximately semicircular shape as shown at 9D.

In the operation of the system shown in these figures, a beam of electrons is projected from the emitter III toward the plate I22 with a velocity depending on the size of the apparatus but corresponding to a few hundred volts or more. through the tube II 3 without undue spreading. If it is formed of substantially parallel rays, it will not be affected appreciably by the magnetic field which, as specified, has its fiux lines parallel to the axis of the tube 3. When a signal of suitable frequency is introduced into the resonator II'I an alternating electric field is produced at right angles to the magnetic field and to the axis of the tube II3. In the drawing the direction of the magnetic flux is indicated by the arrow marked H and the direction of the electric field is indicated by the reversing arrow E. When the alternating field E is present the electrons are alternately accelerated up and down in the direction of the electric field. Their vertical motion which is at right angles to the magnetic field subjects them to a rotating effect of the magnetic field so the electrons move up and sidewlse and down and toward the other side. The result is that as they move through the tube II3 they are subjected repeatedly to simultaneous vertical and horizontal acceleration transverse to their direction of movement and as a consequence are accelerated in a helix of continuously increasing radius. By the time the electrons leave the tube II3 they will have a considerable velocity of rotation and the beam of electrons will rotate as a spot on plate I22 about the axis of the tube H3 and the hole I23. The radius of the rotation will be a function of the strength of the signal introduced into the resonator. Ill. Tube H3 is subjected inside to the effects of space charge resulting from the presence of the electron beam and unless measures are taken to avoid it the The beam is made so it is projectedtube may become objectionably charged on its inner surface. To avoid this we coat the tube inside with a conducting material having high resistance but with sufllcient conductivity to carry away the electrons that stop on the tube surface. This prevents inner surface charge but does not impair the insulation character of the tube generally.

The apparatus is proportioned preferably so that with no signal in resonator II! the beam of electrons goes straight through the hole I23. If a round hole is used as at 9C it is made pref- 'erably of the same diameter as the beam so the beam will just fill it. Then when a signal is introduced the beam begins to rotate and extend partially or wholly beyond the circumference of the hole with the result that less of the electrons go through the hole than when the signal is zero. Consequently the portion of the electrons that go through the hole I23 will be a function of the signal strength. With a strong enough signal the beam may rotate around the outside of the hole missing it entirely. The electrons that enter the hole I23 will produce a field between the plates I 22 and I24 proportional to the number that get through. The variation of this field can be amplified as desired by the amplifier I25. The collection of electrons by the plate I22 produces a unidirectional pulsating current that is a function of the strength of the signal in resonator Ill. The increase in current from plate I22 is accompanied by a corresponding decrease in current from plate I24. This is the condition necessary and sufiicient for signal detection. An alternative form for hole I23 is as shown at 9D as a semicircle. The beam may be adjusted relative to the hole so that it is obstructed by the part of the plate I22 bounding the diameter of the hole I23. Then when a signal is impressed on the resonator II! the electron spot rotates partly or entirely crossing the boundary of the hole and letting electrons enter the hole periodically thus producing a pulsating direct current which may be used for exciting a resonator in the manner shown in Fig. 1, such resonator energizing loop H8. The number of electrons that. go through the hole will be a. function of the signal strength. The shapes of hole described are only two examples of a great variety possible. If a plurality of holes are used in a circle swept by the rotating beam, the frequency of undulations impressed between plates I22 and I24 will be a multiple of the signal frequency of resonator II! and frequencies can be multiplied accordingly.

As many changes could be madein the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of exciting an oscillating circuit comprising a hollow conducting member having an aperture in the wall thereof which consists of producing an electron beam of periodically varying velocity, causing the beam to pass through a deflecting field thereby imparting to the beam a curved course the radius of which is a function of the electron Velocity, thereby causing the beam to oscillate at right angles to its path and encounter the apertured member of said oscillating circuit causing the oscillating beam to periodicallyjenter such member to produce periodic variations in thenumber of electrons in transit in the oscillating c'ircult.

2. The combination of an internallyresonant substantially closed hollow conducting member adapted to contain standing electromagnetic waves, means for producing standing electromagnetic waves therein resonant at the natural frequency of said member, means for producing an electron beam, and means for causing said electron beam to coact with the standing electromagnetic waves within said member to produce periodic controlled deflections of said beam.

3. In combination, an internally resonant conducting member, means for producing an electron beam and for causing the same to pass through said member, said member having an electric vector of contained field perpendicular to the direction of motion of the electrons of said beam for effecting periodic transverse movement of said beam, and a second internally resonant conducting member for receiving said beam after leaving said first member, said second member operating to derive electromagnetic energy from said periodically transversely moving beam.

4. In combination, means for producing an electron beam, an internally resonant substantially closed conducting'member adapted to contain a standing electromagnetic field, means for establishingv said field therein for oscillating at the fundamental frequency of said member, said member having portions of its walls electron permeable, means for projecting said electron beam through said electron permeable wall portions of said resonant conducting member and through a portion of the electromagnetic field contained therein for efiecting transverse deflection of said electron beam.

5. In combination, means for producing a beam of electrons, a hollow internally resonant conducting member having adjacent internally projecting portions and adapted to contain a standing electromagnetic field, means for projecting said beam of electrons between said internally projecting portions, and means for causing said beam to swing laterally between said projecting portions so as to impinge first on one of said projecting portions and then on the other, thereby maintaining an electromagnetic field within said hollow internally resonant conducting member by transfer of energy to the portion of the electromagnetic field existing between said internally projecting portions.

6. In combination, means for producing an electron beam, a hollow internally resonant substantially closed conducting member, means for producing standing electromagnetic waves in said hollow member, and means for projecting said electron beam through said hollow member substantially at right angles to the electric vector of said standing electromagnetic waves for elTecting deflection of said electron beam.

7. In combination, means for producing a beam of electrons, an internally resonant hollow conducting member, and means for passing said beam of electrons through said hollow conducting member along the axis of the electric field therein, to periodically change the velocity of the electrons of said beam, and means for bending said electron beam into an arc, the curvature of which depends on the velocity of said electrons.

8. In combination, means comprising a hollow internally resonant conducting member having a part of the walls thereof electron permeable, means for exciting standing electromagnetic waves therein, said waves having the natural frequencies of said member, means for project ing a beam of electrons through said standing waves, said first named means being orientated with respect to said beam so that the latter is laterally deflected whereby said first named means acts on the beam so that the electrons thereof passing a point after leaving said conducting member periodically vary in velocity with the frequency of said standing waves and take differing paths, and means acting to segregrate the electrons into groups in accordance with the paths followed by the electrons after leaving said resonant conducting member.

9. The method of exciting an oscillating circuit having standing electromagnetic waves.

which comprises producing an electron beam of periodically varying velocity, causing the beam to pass through a field imparting to the beam a curved course, the radius of which curved course is a function of the electron velocity, the varying velocity of the beam causing the same to oscillate laterally with respect to its path, removing the electrons having certain lateral displacements from the beam, at a plane extending at right angles to the path of travel thereof thereby producing an electron beam from that plane on that is of periodically varying density, and causing said beam of varying density to enter and deliver energy to the standing electromagnetic waves of the oscillating circuit.

10. The combination of means for producing a beam of electrons, means for producing an oscillating electric field acting along the axis of said beam to periodically change the velocity of the electrons of said beam, means for bending said beam into an arc, the curvature of which are depends upon the velocity of the electrons of said beam, and means for segregating the electrons of said beam into two groups depending upon the curvature of their arcuate paths.

11. In apparatus of the kind described, means for producing a divergent beam of electrons emanating from a region of high electron density, means for forming an electron image of said region of high electron density at a distance from said region of high electron density, said distance depending on the velocity of said electrons,

a hollow resonator interposed between said region of high electron density and said image thereof in the path of said beam for periodically varying the velocity of electrons passing from the region of high electron density to the said image thereof, and means for segregating the said electrons into groups according to the distance from said region of high electron density at which particular electrons form an image.

12. The method of converting the kinetic energy of a cathode ray beam into oscillatory energy of high frequency, which comprises passing a beam of electrons through a confined and sharply bounded system of standing electromagnetic waves to produce oscillatory lateral deflection of said beam, and then passing said beam through a second confined and sharply bounded system of standing electromagnetic waves for delivery of energy to said system of standing electromagnetic waves.

13. The combination of means including an internally resonant substantially closed hollow conducting member adapted to contain standing electromagnetic waves, means for producing an electron beam and means interposed between said member and said beam producing means for effecting periodic controlled deflections of the beam, said member being apertured for receiving said deflected beam to thereby set up and maintain standing waves within said member.

14. In high frequency apparatus of the character described a hollow substantially closed conducting member, means for setting up a standing electromagnetic field within said member, and means for producing and projecting an electron beam through said member for efiecting velocity changes of the electrons of said beam and lateral deflection thereof for use in deriving energy therefrom.

15. In apparatus of the character described,

means for producing an electron beam, a hollowconducting member, means for exciting a resonant electromagnetic field in said member, means including accelerating means for projecting said electron beam through said member and for causing periodic lateral displacement of the electrons of said beam from their mean positions at the frequency of said resonant field, and

' means for segregating said electrons into groups according to their lateral displacement.

16. The method of controlling and segregating electrons at high frequency characterized by multiply and coherently reflecting electromagnetic waves back and forth in a confined space,

RUSSELL H. VARIAN. WILLIAM W. HANSEN. LINDSAY M. APPLEGA'I'E. 

